Moving handrails in escalators and moving walkways can be driven with a number of different drive assemblies. An important feature, however, of any handrail drive assembly is that the handrail be driven at a speed which is very close to the speed of the steps or treads, and that the handrail stop moving when the steps or treads stop moving. This result is typically achieved by tying the handrail drive to the step drive by means of a drive chain which is driven by the step drive and which drives the handrail drive. The handrail may be driven by passing it through a roller nip; by a single biased driven roller; or by a belt or rollers which engage the inner surface of the handrail.
The use of a roller nip is not preferred since the rollers squeeze and deform the handrail. The exposed outer surface of the handrail can be damaged by this type of drive. An additional problem relating to a nip drive concerns the fact that the two opposite surfaces of the handrail will possess different coefficients of friction, whereby one of the rollers will typically slip on the handrail. The reason for this is that the underneath side of the handrail will be partially formed from a slippery or low coefficient of friction material so that it can slide easily over its guide rail. Additionally, a nip drive will cause a kink in the handrail as it passes through the nip, which lowers the operational life of the handrail.
Single biased drive rollers do not create some of the problems that a roller nip drive does, however, they still require arcuate deformation of the handrails as they pass over the drive roller, which will ultimately weaken the handrail. In addition, this type of drive will be rendered inefficient over time as the handrail stretches.
Handrail drives which contact only the inner or underneath surface of the handrail are desirable because they do not touch and cannot mar the external surface of the handrail on which the passengers rely. In addition, handrail drives which contact the handrail in a linear fashion are also highly desirable, because they do not subject the handrail to harmful bends or localized compression. Inner surface handrail drives have been proposed, but one problem that they all face relates to the fact, mentioned previously, that part of the inner surface of the handrail is intentionally made slippery so that it can slide over the handrail guide rail without generating excessive heat. How to ensure a sufficiently tight driving engagement between the drive mechanism and the handrail is the problem encountered. U.S. Pat. No. 3,283,878, granted Nov. 8, 1966 to L. R. Rissler discloses an inner surface handrail drive system which includes a drive belt that contacts the handrail through the newel portion of the escalator, and which relies on the inherent tension in the handrail as it passes over the newels to press the drive belt and handrail together. U.S. Pat. No. 5,117,960 granted Jun. 2, 1992 to H. W. Ahls, et al. discloses an inner surface linear handrail drive system which relies on a series of presser rolls to force the drive belt against the inner surface of the handrail. Both of the latter systems result in minimal damage to the handrail.